1. Field of the Invention
The present invention relates to a microwave calorimeter for very high power, with a housing which surrounds a feed chamber into which a waveguide runs for feeding the microwaves, and an absorber-chamber which is separated from the feed chamber by a dielectric wall and contains a microwave-absorbing fluid.
2. Description of the Prior Art
There is known from U.S. Pat. No. 4,593,259 a microwave calorimeter for very high microwave power, which encloses an inner, cylindrical feed chamber (into one of the front sides of which a waveguide runs for the feeding of the microwaves) and an absorber-chamber surrounding the feed chamber like a jacket. The absorber-chamber is separated from the feed chamber by a dielectric wall, and it contains a microwave-absorbing fluid, namely, water. A coaxial cone-shaped reflector projects from the front wall of the feed chamber which lies opposite to the mouth of the waveguide, and this reflector reflects the microwaves which are fed axially through the waveguide outwardly to the absorber chamber.
Since the depth of penetration of the microwaves is continuously less with increasing frequency, such a "water load" has the disadvantage that the microwaves are finally absorbed only in a very thin water layer bordering on the dielectric wall, whereby at high power there can result bubble formation and boiling of the water in this thin layer. This leads in turn to a strong reflection of the power, whereby under certain circumstances the microwave generator (e.g. a gyrotron) and/or the absorber can be destroyed. It has been attempted to overcome this disadvantage by allowing the water to flow with high flow speed through the absorber chamber, in order to prevent the formation of vapor-bubbles or to remove along with the stream the bubbles which arise. However, this makes exact calorimetric measurements more difficult and in many cases it is not practical.